1. Field of the Invention
The exemplary embodiments are related to a substrate processing apparatus, and in particular to substrate processing apparatus handling non-productive workpieces.
2. Brief Description of Related Developments
One of the uses of conventional sorters is in the introduction of non productive workpieces (NPW) such as wafers or other test flat panels into the processing system, such as for example, production lots, test, qualification or filler wafer lots. Generally, in conventional systems, test panels, such as NPWs are held in carriers located or stored away from the sorter and transported to and from the sorter when used.
U.S. Pat. No. 6,336,546 describes one example of a conventional conveying system configured to transport carriers, such as flat panel cassettes, or for example, Front Opening Unified Pods (FOUPs)) containing semiconductor wafers to a plurality of processing centers. In this example, the conveying system lines up a series of carriers that store and index wafers at the processing centers.
PCT Patent No. WO 02/03424 A1 describes an example of a conventional storage and buffer system for cassettes containing semiconductor wafers consisting of two adjacent conveyor lines along which the cassettes move. One conveyor line serves as a transport row for cassettes and another serves as a storage row for cassettes. The conveying system also includes a means for rotating the cassettes such that they can be moved from the transport conveying row to the storage conveying row and vice-versa.
As seen from the above examples, in conventional processing systems, carriers with non-productive test workpieces are stored away from the sorter and are brought to the sorter/processing tool along with empty or partially filled carriers to which the non-productive wafers are added. Storage of non-productive test wafers away from sorter increases the time used to sort the non-productive test wafers into a destination carrier, which limits the productivity of the conventional semiconductor processing center. Further, placement of transport carriers of NPW onto a holding station(s) of sorter/processing tool(s) displaces carriers of production workpieces from the holding station(s) of the sorter/processing tools.